Generally, a pneumatic tool applies compressed air to drive a built-in air motor and consequentially a tool. Discharge of compressed air from a pneumatic tool always results in a loud and uncomfortable noise because of the strong force of the air flow. In view of this problem, the inventor created a noise suppressor of new structure for a pneumatic tool. It includes some suppression grooves on an inner wall of the the body of pneumatic tool to disturb compressed air flow and to cause a collision of compressed air with the groove so that noise caused by the air flow is greatly reduced. Its structure is simple and practical.